I really like all of it, with a few suggestions. Note: I attempt (attempt, I might be bad at this) to keep from viewing everything as an experienced player and will just look at the concept of things. As for difficulty, I will try to view it not as someone who has played for 1 and 1/2 ish years.

"* The new monsters! Difficulty, behavior, how can we improve them?"

The new monsters are perfect, or at least their intention. Their attacks, their difficulty, all of it is good, if anything they could be made a bit more difficult and swarmier. A swarming type of monster that dies fast is something that will improve combat in this game and give the incentive for bombing.

Bombers will rip them apart. Bombs now have a great purpose. You guys needed to do something great for bombers especially after the shard bomb change, and this is it.

Gunners (woot woot!) and guns in general needed a soft counter. This was perfectly done, great job. Gunning in this game was too easy (although it takes longer, doing runs without taking damage wasn't a rare occurance), and a swarming type monster is just what needed to soft counter guns without being too difficult.

Swords are still swords: their slashy nature will prove great against them, but they will still be the more dangerous route to approach the swarming monsters.

Suggestions: none, I like it how it is. Possibly make swarm monsters slightly more durable, otherwise it's all good.

"* The new levels! Difficulty, payout, any bugs you encountered."

Difficulty is appropriate, I wouldn't say it was too hard and the diversity ensures that they are not too easy. I didn't encounter any bugs personally.

Suggestions: As for payout, I would say make sure that the swarm monsters give some sort of payout unless they are the respawning ones (even if it is small) to give players the incentive to face the swarm down. I truly want bombers to have this great use, and if we just pass up swarm monsters and ignore themdue to no loot that will not be good for bombers.

Please add these into the arcade! Arcade is what this game used to be - always changing etc. This would be a perfect arcade level / theme to improve + make the arcade more fun rather than only added into missions.

" * Thoughts about the UI?"

It is all great, I like how things are being changed up with monster diversity and different UI. Now all we need is changing weather in Haven + night / day as well as new music! /wink

Suggestions: I would make the Shield bar a little smaller ;) And rather than "advance" when going down the elevator, I would personally have it say "descend" but that's pretty nit picky. It just sounds scarrier for someone to "descend" and not quite as scarry when they are "advancing"